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Agronomy notes
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Permanent Link: http://ufdc.ufl.edu/UF00066352/00090
 Material Information
Title: Agronomy notes
Uniform Title: Agronomy notes (Gainesville, Fl.)
Physical Description: v. : ill. ; 28 cm.
Language: English
Creator: Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Place of Publication: Gainesville
Creation Date: July 2007
Subjects / Keywords: Crops and soils -- Florida   ( lcsh )
Crop yields -- Florida   ( lcsh )
Agriculture -- Florida   ( lcsh )
Agronomy -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
periodical   ( marcgt )
serial   ( sobekcm )
Statement of Responsibility: Florida Cooperative Extension Service, University of Florida, Institute of Food and Agricultural Sciences.
General Note: Description based on: January 1971; title from caption.
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Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000956365
notis - AER9014
System ID: UF00066352:00090


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Vol. 31:7 July 2007

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Quick Field Test for Nitrates in Corn and Summer Forages ........................................... 2

Control of N utsedge in Cotton ..................................................................... .....................
Timing of Nitrogen on Cotton .......................... ...... ......................................... 2
When is Too Late to Make a Good Cotton Crop? ............................. .......................... 3

R rotating C rops w ith B ahiagrass............................................................................ 3
Nitrate and Prussic Acid in Forages Beware this Year..................................................3
K keeping the Forage Calendar................................................ ................................ 4

Peanut Problems .......................... ........................................ 4

Increase of Soybean A creage ......................................................................................... 5

M axim izing Sm utgrass Control ............................................. ............................... 5

Late Planting Dates for Peanut, Soybean, Cotton, Corn, and Sorghum............................. 6
Planting Another Crop After a Drought Stressed Crop ................................................ 6

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Employment Opportunity _Affirmative Action Employer authorized to
provide research, educational information and other services only to individuals and institutions that function without regard to race, color,
sex, age, handicap or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension
Office. Florida Cooperative Extension Service/ Institute of Food and Agricultural Sciences/ University of Florida/ Larry Arrington, Dean.

Quick Field Test for Nitrates in Corn and
Summer Forages

Livestock are sensitive to high nitrates in
grass crops and care should be taken in
grazing summer annual grasses during
drought periods. Nitrates are usually highest
in the base of the stalk and become less
concentrated as you get higher on the plant.
Plants that have died from drought may have
high nitrates in the lower stems and if cut for
hay or silage they may need to be cut high to
reduce the likely hood of high nitrates.
After periods of drought, plants should be
checked for nitrates before being utilized.
Nitrate test can also be used to determine if
nitrogen is adequate for corn growth during
the vegetative stage of growth. Making the
Solution for Testing: Dissolve 1 gram of
diphenylamine in 100 ml of concentrated
sulfuric acid. This solution is very corrosive
so be careful when handling it. If the
solution becomes discolored, prepare a new
one. A small bottle with a dropper will be
enough to test many plants. Testing
Methods- To test for nitrates, cut stalks of
corn, millet, etc., and slice the stem in half,
length wise. Apply a few drops of the
solution of sulfuric acid with the
diphenylamine along the split stem, from the
base to the top. Where nitrates are present, a
blue color is produced immediately on the
stem tissue. Dark blue color indicates high
amounts of nitrates. If no blue color is
produced, no reserve nitrates are present and
the yellowish green color indicates that
nitrogen is inadequate for normal growth.

David Wright

Control of Nutsedge in Cotton

Nutsedge has been a problem in cotton for
many years. Even with all the advantages
that Roundup Ready cotton provides,
nutsedge is one weed that glyphosate often
fails to control. So what are our options?

In small cotton there are still few choices.
The best solution is to spray glyphosate
while the nutsedge is small. Even if the
glyphosate application does not kill the
weed, it will often cause severe injury and
delay its growth for 2 or more weeks. This
period of time is generally sufficient to
delay the nutsedge until a more effective
follow-up application can be made. We do
not commonly recommend using MSMA
broadcast since nutsedge control is marginal
and cotton injury is often excessive.

For larger cotton, there are more options.
Envoke is extremely effective on nutsedge
(even large plants) and can be applied over-
the-top of cotton after the 5th leaf stage.
Envoke can be injurious to small cotton, but
tolerance improves dramatically after the 5th
leaf stage and the plant continues to become
more tolerant with age. Another option for
larger cotton is glyphosate+MSMA applied
as directed. This combination, when applied
below the cotton leaves, provides excellent
nutsedge control without excessive cotton

At layby, Suprend herbicide is an excellent
choice. Suprend is a combination of Envoke
+ diuron. Of important note, Suprend is
price competitive to Envoke alone; meaning
that the added benefit of the diuron is
essentially free.

By taking advantage of the herbicides now
at our disposal, highly effective nutsedge
control can be obtained.

Jason Ferrell

Timing of Nitrogen on Cotton

Normally nitrogen is applied to cotton
during late squaring to early bloom. Cotton
does not require as much N as many crops.
Normally 50-60 lbs/A are required for a bale
of cotton. However, there may be 20-50

lbs/A ofN available to the plant over the
season in the soil and applications of 60-90
lbs/A of N may be adequate for 2-3 bale
yields. Sandy soils do require more N than
heavier soils since there is usually less
residual and lower amounts of organic
matter. Nitrogen should be applied to cotton
no later than the 3rd week of bloom. Sulfur
is especially important on sandy soils with
yield responses of a bale per acre (with 30
lbs/A of S). Late foliar applications ofN as
urea are not recommended unless there is
not a good boll set.

David Wright

When is Too Late to Make a Good Cotton

This is the slowest that I have seen cotton
grow off. There are usually rains at some
point before this time of year and cotton is
often 15-30" tall by now and in a rapid
growth stage. Is it too late to try to make a
good crop and should inputs be reduced?
Normally cotton will begin blooming in the
first or second week of July if planted
timely. However, cotton will still make a
good crop if it starts blooming by the first
week of August. Therefore, inputs should
be put into the crop to make good yields.
Cotton is very drought tolerant due to the
long bloom period (usually 8 weeks or
more). If cotton can have 4 good weeks of
bloom until early September, high yields can
still be made. Many fields have very uneven
plant heights due to cotton germinating over
a period of 4-6 weeks. It will take a few
weeks of good rains for the crop to catch up
in height. When the crop has even out, then
it can be managed better than during the
drought that we encountered.

David Wright

Rotating Crops with Bahiagrass

Since the first half of 2007 has started out
very dry, this would be a good year to

consider planting bahiagrass for rotation
with other crops especially if other crops
have failed and the outlook for other cash
crops is not bright. Our research results
have shown that bahiagrass in rotation with
other crops can enhance soil properties
including organic matter as well as reduce
pest pressure for subsequent crops. We have
seen as much as 2-7 fold increase in returns
to the farm if bahiagrass is included in a
farming system and cattle can add
significantly to the profit potential.
Perennial grasses weather the storms and
droughts better than annual crops; perennial
crops can still produce well after weather
extremes while annual crops normally have
a period of several weeks when adequate
moisture is very critical to achieve high
production. If the plant does not receive
adequate moisture in the critical period, it
cannot recover. Fields that are in bahiagrass
or other perennial grasses for 2 years can be
utilized for grazing, seed production, hay, or
biomass for bioenergy. Most of the
perennial grasses will produce high amounts
of forage if irrigated and fertilized well.

David Wright

Nitrate and Prussic Acid in Forages -
Beware this Year

Nitrate and prussic acid in forages are not
the same but both may have fatal
consequences to livestock and they occur
under similar conditions. I will go over each
of the toxicities and their differences. First,
nitrate poisoning: To some extent nitrate is
present in all forages. Technically, the
problem with nitrates occurs when nitrate
concentrations in the plant are unusually
high, usually when the plants undergo
drought conditions like the ones we have
had this year. Drought conditions impede
the plant from growing at the normal rate
and the nitrogen absorbed by the plant,
instead of being converted into new growth,
accumulates in the plant at toxic levels for
livestock. Plants that accumulate nitrates

are those in the sorghum family (forage
sorghum and sorghum hybrids, Johnson
grass), corn, bermudagrasses, leafy
vegetables, pigweed or carelessweed
(Amaranthus). Special care must be taken
when holding animals in pens where
pigweeds are present because animals will
consume these weeds and sudden poisoning
can result (in many cases within 4 hours of

How to prevent losses? Do not graze during
stress periods and monitor nitrate levels to
determine if the levels in the forage are safe.
Do not graze forages of the sorghum family
too short; nitrates accumulate in the older
lower leaves. If you test the forage and
nitrate concentrations are high, keep in mind
that once the concentration is high they
remain high; curing the forage does not
minimize the concentration as is the case
when prussic acid is present. One alternative
to using forage with high nitrates is to dilute
the nitrate concentration by feeding hay that
does not have any nitrate problem. The
toxicities guidelines show that ruminants in
general can safely eat forages that have up to
1% of nitrates on a dry weight basis. Horses
are thought to have a higher tolerance to
nitrates but keeping the cattle guidelines for
horses is a safe measure.

Prussic acid, this is another problem that is
present with drought conditions. It also
occurs in plants of the sorghum family,
commonly less than 1 12 foot, and
occasionally on white clover but prussic acid
does not occur in pearl millet or corn.
Different from nitrate poisoning, prussic
acid accumulates in the new growth and not
in the older lower leaves. Prussic acid
poisoning occurs within minutes of
consumption and is one of the most toxic
conditions. Livestock may show symptoms
of intoxication within minutes after
consumption of feed. Different from nitrate
poisoning, prussic acid dissipates or goes
away when the hay is properly cured
because the toxic compound volatilizes over

time. However, you still need to monitor the
hay and have it tested for prussic acid to
confirm 'safety' in using the feed. After a
rain or irrigation on drought stressed fields
wait at least 2 (two) weeks after plants begin
to grow before grazing.

Yoana Newman

Keeping the Forage Calendar

Keep in mind that to obtain that high quality
bermudagrass hay or forage for grazing you
need to keep up with the "forage calendar".
Observing the forage calendar is not difficult
or complicated and just implies to cut or
graze your perennial warm-season grasses
(bahiagrass, bermudagrass, hemarthria or
limpograss, stargrass) when they are 4 to 5
weeks old. Grass cut at 4 to 5 wk old
maturity will have high digestibility and
crude protein for beef cows and horses.
Cutting or using the forage at a later time
means you will be harvesting or providing
your livestock mainly with fiber and with
little nutritive value. Warm-season
perennial grasses beyond 35 days sharply
drop in nutritive value. Cutting or using
your grass earlier than 35 days will increase
not only the quality but the productivity of
your grass.

Yoana Newman

Peanut Problems

Peanuts may have a yellow cast to them
during the growing season at times. There
could be several causes for this yellowing.
Some of the causes include poor nodulation,
micronutrient deficiencies, or herbicide
damage. Other fields have been planted
after other crops have been grown and the
newly planted fields have encountered
seedling diseases which results in plants
dying and not much discoloration.
Manganese deficiencies may occur on soils
that have been limed for years and have a
pH above 6.3. Manganese applications will

be needed for the crop to over come this
deficiency. It is possible to lower the pH
through acid forming fertilizers, however,
applications of a few pounds of Manganese
sulfate micronutrient may be more cost
effective for that crop and the response will
probably be quicker than trying to change
the pH rapidly.

David Wright

we know that the disease will be a problem.
Fungicide applications are not normally
made until bloom period which usually
occurs in July and August depending on
planting date and maturity group. We have
been very successful with MG V soybeans
planted in August for crop maturity times
and yield.

David Wright and Jim Marois

Increase of Soybean Acreage

Due to the failure of corn, cotton, and
peanuts in many areas across Florida, there
has been a big surge in interest in soybeans
which may be planted as late as mid to late
August. However, with late planting the
possibilities increase for a problem with
Asian soybean rust (ASR). Research at
NFREC in Quincy over the past 3 years has
shown that the disease is much more intense
late in the season and therefore we plant
many of our studies in July and August. The
disease can be controlled fairly easily with
timely fungicide applications and good
management. Many scientists from the
eastern half of the US are working on
soybean rust in Quincy. There is a web site
http://www.usda.gov/soybeanrust/ devoted
to the disease and its spread. The website
also features a weekly commentary obtained
from sentinel plots that have been planted all
over the US in soybean producing states.
The disease has not spread as rapidly as in
the past 2 years due to the very dry
conditions. However, with late planted
soybeans it is still early in the season. If
ASR spreads and the disease incidence is
severe, fungicides will be recommended for
control. At the current time the disease has
only been found in sites in central Florida
and in Jacksonville and in sites in Louisiana
and Texas. This can change very rapidly
with rainfall and movement of spores on
storm systems. Counties will be notified as
the disease appears and information will be
passed on to growers. Fungicides are not
being recommended at the current time until

Maximizing Smutgrass Control

Smutgrass is an all too common pest that
infests 1,000's of acres in Florida and across
the Southeast. Although tropical soda apple
and Brazilian pepper often get more
attention, smutgrass is more common and
costly than any other pasture weed in
The reason smutgrass is so common is that
control can be costly and tricky. However,
there are certain strategies that can
dramatically improve smutgrass control.

Herbicide Selection. Currently, Velpar is
the only herbicide that will consistently
control smutgrass. Much work has been
done to determine the optimum application
rate to minimize cost while maximizing
control. Research has shown that Velpar at
2 pt/A can control smutgrass, but control
failures are common unless environmental
conditions are just right. Therefore, the
IFAS recommendations are to use a
minimum of 3 pt/A. Our research, over
many locations and many years, have found
3 pt/A to be lowest application rate that will
consistently control smutgrass.

Roundup (or other glyphosate containing
products) will control smutgrass, but it will
also completely kill the desirable forage.
Unless total pasture renovation is desirable,
glyphosate should not be used.

Application Timing. The most critical
component to effective smutgrass control is
proper application timing. Velpar is a soil

active herbicide that is primarily taken up by
plant roots. Therefore, Velpar should be
applied when root uptake will be
maximized. This means that Velpar is most
effective when applied once rainfall is

Applications of Velpar during the dry period
of spring will often fail to control smutgrass.
This failure occurs because rainfall is not
available to move the herbicide into the soil
for uptake by roots. The herbicide then
begins to degrade in the soil and is not
present when the summer rains begin. Our
experience with Velpar is that optimum
smutgrass control occurs when the
application is made in the June to August
timeframe. During these months afternoon
rain is common and smutgrass is actively
growing. Under these conditions, >90%
smutgrass control is commonly achieved.

Other Factors. Other recommendations for
smutgrass often include mowing prior to the
herbicide application. Although this
practice is common, our research has not
shown a benefit to mowing prior to Velpar
application. Considering the current price of
diesel and the time required, mowing is an
unnecessary expense.

It is also common for landowners to include
various adjuvants (surfactants, stickers, etc.)
when spraying Velpar. However, our
research has shown that these adjuvants are
not necessary. The purpose of an adjuvant
is to improve herbicide uptake into plant
leaves. However, most Velpar activity is
through root uptake, with only minimal
amounts entering the leaves. Granted, leaf
uptake of Velpar does occur and in some
conditions an adjuvant may improve control.
But, if Velpar is applied in the summer
months, when rainfall is common, smutgrass
control will be maximized and the use of an
adjuvant is not necessary.

Smutgrass is a difficult weed, but it can be
managed. Applying the correct herbicide,

using the proper rate, and applying at the
right time will kill smutgrass and give you
more bahiagrass to graze.

Jason Ferrell and Brent Sellers

Late Planting Dates for Peanut, Soybean,
Cotton, Corn, and Sorghum

Soybeans may still be planted in July and
August if drilled and irrigated. Yields can
be very satisfactory with MG V-VII. This
may seem like a big turn around from 15
years ago when we would recommend late
MG soybeans for late planting. However,
since we have been working on Asian
soybean rust, we have found the MG V
soybeans can yield 35-50 bushels when
planted late and managed properly. They
will normally mature before a frost and set
seed and fill pods during longer daylength
periods with less irrigation. Peanuts will not
yield enough to be profitable from plantings
made in July. Also, peanuts are often
damaged from late frosts when dug in
November. If planted in July, cotton will
not make developing bolls because of
potential freeze. Corn may be planted as a
second crop for grain or silage if a Bt hybrid
with good disease resistance or a good
tropical hybrid with Bt are used. The latest
planting date for corn should be July 15-20
to make satisfactory yields. Grain sorghum
can be planted as late as corn with good
silage yields.

David Wright

Planting Another Crop After a Drought
Stressed Crop

It is tempting to turn around and plant
another crop immediately after other crops
have failed. However, be very cautious
since residual herbicides can result in poor
plant growth or death of the following crop
if the plant back restriction is not followed.
Also, when planting a crop into the green
residue of the previous crops, plant diseases

can be a problem on seedlings of the newly
planted crop. Seedling disease is always a
problem with cotton, peanut and soybean if
the cover crop or previous crop is not killed
far enough in advance or if heavy residue is
incorporated into the soil. It would be best
to wait for 3-4 weeks or more before the

next crop is planted into a crop that had
green residue or use strip tillage with in
furrow fungicides to help combat seedling

David Wright

The use of trade names does not constitute a guarantee or warrant of products named and does not signify approval to the exclusion of similar
Prepared by: J.M. Bennett, Chairman i,,h1, ,,11 ...I, J.A. Ferrell, E -1, ... ._,...1...11. i, 11 Iinl, .1, ,, 1 .1.. Jim Marois, Plant
Pa. III.._I i .j. ...i ,,11 i.I, Yoana Newman, Extension Forage Specialist ., ,,il ..h B.A. Sellers, Extension Agronomist
II., I., ,i, ,,1i .1,, D.L. Wright, Extension Agronomist IJdl\\ aifa,.ufl.edu .